1. Field of the Invention
The present invention relates to a data backup apparatus and, more particularly, to a data backup apparatus for holding stored data using an internal battery when the main power is stopped.
2. Description of the Related Art
With the recent development of IC fabrication techniques, ICs have come into frequent use for household electric appliances as well as electric appliances for business use. In many electric appliances, the user can store his own data in an IC memory to utilize various facilities. For example, a volatile memory which is provided in a facsimile machine or a system telephone equipped with an answering machine (hereinunder referred to as "answer phone") can store the data exclusively for the user such as abbreviated dialing codes, an identification number and an answering message. The abbreviated dialing code is composed of about 3 digits as which a frequently used phone number is registered, and it is possible to call up the registered phone number merely by pressing the keys for the abbreviated dialing code. The identification number is a password identifying the user when the user operates the answer phone from an external telephone through a telephone line. The answering message is a message conveyed when the answering machine is operated.
In this way, by storing the data exclusively for the user into a volatile memory by the user, it is possible to simplify the operations of mechanisms which are frequently used or to automatically operate the machine from an external machine.
Volatile memory generally has a simpler structure than a nonvolatile memory, so that a volatile memory enables low cost production and a reduction in size. In addition, since a volatile memory allows partial reloading and is easy to operate, it is effectively utilized for an apparatus in which change or addition of the stored contents is frequent.
Such a volatile memory is operated and the data stored therein is held by the main power which is used for driving an entire facsimile machine or an answer phone equipped with the volatile memory. When the supply of the main power is stopped such as when power stoppage happens or when the attachment plug is pulled out, the internal battery provided in the facsimile machine or the answer phone temporarily supplies power as the backup power source so as to drive the facsimile machine or the answer phone and to hold the data stored in the volatile memory.
Long term backup, however, is impossible using a conventional internal backup battery, when the performance thereof is considered on a cost/performance basis.
In other words, a conventional internal backup battery cannot continue to supply power when the main power is stopped for a long time and the internal battery dies. When the facsimile machine or the answer phone is so frequently operated during the operation of the internal battery that the internal battery dies, it is also impossible to continue to supply power. In such cases, it is sometimes impossible to supply power necessary to maintain the backup of the data of the volatile memory which stores important information. As a result, all the important information stored in the volatile memory is lost. Consequently, even after the supply of the main power is restored, the telephone numbers registered as the abbreviated dialing codes are lost, thereby making it impossible to use the abbreviated dialing function. The identification number is also lost, thereby making it impossible to use the remote controlling function, and the answering message of the answer phone is lost, thereby making it impossible to use the function of the answering machine. The troublesome operations of restoring the abbreviated dialing codes, the identification number and the answering message are therefore necessary after the supply of the main power is restored.